Falling developer curtain printing and coating

ABSTRACT

Method and apparatus for creating a falling curtain of toner adjacent to a vertically disposed stencil screen for printing or coating a vertically disposed surface of a substrate. By creating the falling curtain between a pair of spaced stencil screens, two substrates can be simultaneously coated or printed. Non-planar objects can be printed or coated by providing a non-planar stencil screen.

United Rarey et a1,

tes Patent r1 1 [111 3,776,132 51 Dec.4, 1973 FALLING DEVELOPER CURTAIN PRINTING AND COATING [75] Inventors: Kenneth W. Rarey, South Holland;

' John B. Kennedy, Jr., Oak Forest,

both of Ill.

[73] Assignee: Continental Can Company, Inc.,

New York, NY.

22 Filed: Feb. 1,1971

[21] Appl. No.: 111,233

[52] US. Cl 101/129, 101/114, l0l/D1G. 1'3 [51] Int. Cl B4l'm 1/12, B41f 15/00 [58] Field of Search IOI/DIG. 13, 114, 101/ 129, 35

[56] References Cited UNITED STATES PATENTS 3,266,046 8/1966 Boyd 101/D1G; 13 3,320,879 5/1967 Edwards et al. l0l/DIG. 13 2,930,351 3/1960 Giaimo 10l/DIG. 13 3,081,698 3/1963 Childress et a]. l0l/DIG. 13

3,238,053 3/1966 Morgan 101/DlG. 13 3,302,561 2/1967 Edwards 101/114 X 3,302,579 2/1967 Edwards et a]. .t l01/DIG. 13 3,306,193 2/1967 Rarey et al. l01/DIG. 13 3,340,802 9/1967 Pilon lOl/DIG. 13 3,418,930 12/1968 Rarey et a]. 101/114 3,473,467 10/1969 Johnson et a.l.... lOI/DIG. 13 3,487,775 l/1970 Chaney et 101/DlG. 13 3,521,558 7/1970 Fisher et al. l0l/DIG. '13 3,529,546 9/1970 Kollar 101/426 Primary ExaminerEdgar S. Burr Att0rney Diller, Brown, Ramik & Holt [57] ABSTRACT Method and apparatus for creating a falling curtain of toner adjacent to a vertically disposed stencil screen for printing or coating a vertically disposed surface of a'substrate. By creating the falling curtain between a pair of spaced stencil screens, two substrates can be simultaneously coated or printed. Non-planar objects,

can be printed or coated by providing a non-planar stencil screen.

4 Claims, 9 Drawing Figures PATENIEDBEE 4191a 3.776.132

' sum 3 OF 3 \YNVENTDRS KENNETH u). QQIZEY Q9-JOHN B. Keuuaomnmmpnsvs BACKGROUND OF THE INVENTION been previously accomplished by methods and apparatus disclosed in U. S. Pat. No. 3,306,193, issued in the names of the present inventors; in U. S. Pat. No. 3,081,698, issued in the names of Childress et al.; in U. S. application SenNo. 386,182 filed on July 30, 1964 in the name of JohnB. Kennedy, Jr.; and in U. S. application Ser. No. 386,183, filed on July 30, 1964 in the name of Kenneth W. Rarey.

In the prior art print-ing apparatus wherein the stencil screens are horizontally disposed, toner or developer is introduced beneath the stencil screen. Asa result, the: toner or developer is actedupon by gravity thereby re,-' quiring relatively high voltages, for causing, upward movement of the toner or developer duringthe. printing; operation or, conversely, the spacing between, the, sub-- strate and stencil screen must be reduced. Gravita-- tional force impedes the oscillation oftoner or (level-- oper betweenthe base electrode, and the stencil-screen;

and, in addition, only'the top few layers of toner ordeveloper oscillate thereby Iimiting'the-rate, of; deposition.

of toner upon the substrate.

SUMMARY or THE INVENTION The present invention providesa. falling curtain-ofa toner or developer wherein gravitational force, rathen than being animpediment, is advantageously utilized? for movingv the toner or developer through the printing;

zone. Greater toner depositionratestare' availableas; compared to the prior art devices. lf;greaterdeposition. rates are not neededthe additionalfflexibility. may beused I in one or more ways. C For example, prihtingor coating time may be reduced; or printingend icleaning voltages may be reduced; or developer;concentration may be lowered. Decreasing both theprinting time and.

printing voltage will reduce anytendencyforarcing be- The present invention provides a falling curtain of toner or developer which oscillates in an electric field established between a vertically disposed stencil screen and base electrode or between a pair of vertically disposed stencil screens. 1

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatical, vertical section showing essential elements of one embodiment of the invention.

FIG. 2 is a perspective view of one form'of printing or coating apparatus. FIGS. 3, 3a and 3b are diagrammatical, vertical sections showing another embodiment of the invention and modifications thereof wherein a pair of stencil screens are used for printing or coating a pair of substrates using either direct or alternating current.

FIG. 4 is a perspective view of a third form of printing apparatus.

FIG. 5 is a vertical section of elements which are used with the apparatus shown in FIG. 4.

FIG. 6 is a horizontal section through a central portion of FIG. 4 after the elements of FIG. 5 have been positioned therein.

FIG. 7 is an enlarged vertical section of the top portion of the apparatus shown in. FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A basic'embodiment of a falling curtain printing and coatingapparatus, generally indicated by the numeral- 10,, i's-shown in FIGS. 1' and 2. A base electrode 12 and aback electrode 14' are shown as being comprised of a pair of conductive plates located in a substantially cally arranged stencil'screen 20 is disposed between electrodes 12 and 14 and is connected across power source. 16 by a voltage divider 22. Stencil'screen 20 v maybe comprised ofa fine wire-mesh screen, of aptween the-base. electrode and-the stencil gscreenyalso,

by, decreasing the printing or, coatingtime, the present i invention increasesthe numberof objectsorsubstrates that can be printedin a given period of time. An ahcilI- lary,benefi t .to decreasing; the developer concentration- 1 is that the amount of toner dustingisdecreased during,

normal handling.

The present invention {also providesfor; printing of non-planar surfacessuch as. annulartorcylindrical 10bjects which can be printed; all the way aroundssincethe; substrate and stencil screen areat rest during the print ing operation, any smearingdue torelativemotionbe tween them is prevented. I

Further, in oneformof the invention,.the number of T object- Printed in-a givenperiodof timeisf doubled becausetwo objects can beprinted'at thesametimeby;v

the single falling curtain of toner.

proximately, 325 mesh, having areas thereon blocked bysuitable masking material 24 soas to provide openings 26 which define the desired pattern for printing or coating. v

A substrate 30 is shown as being comprised of a vertically disposedsheet of'non-conductive material slidably-mounted upon a'pair of guides 32 for movement into and out of apparatus 10.

A reservoir 36 is disposed above apparatus 10 and is providedwith an-elongated slot 38 located above an elongated slot 40 in -a slidably mounted adjustment plate.42'.. As-is shown in FIG. 1, reservoir 36 may contain-a developer mixture 44, such mixture being com'- prised of electrically conductive carrier particles and electricallynon-conductive toner particles; however, it isto be understood that reservoir 36 might also containtoner particles which are electrically,conductive.

A printing operation is performed: by suitably positioning substrate 30 between stencil screen 20- and back electrode 14, and closingswitch- 18 to create ahorizontally oriented electric field between base electrode. 12v and stencil screen- 20.; Plate 42 may be ad" justed so as toalign slots 38 and 40 so that carrier particles and/ortoner particles fallfrom'reservoir- 34 in the formofa free falling curtain. The electric fieldbetween' base electrode .12 and stencil'screen20 causes the developer mixture, or conductive toner, to oscillate back and forth therebetween in the same manner as disclosed in U. S. Pat. No. 3,306,193. Carrier particles are precluded from reaching substrate 30 by the size of the openings in the wire-mesh screen while toner particles 46 can freely pass through openings 26 and impinge upon substrate 30. It will be apparent that a second horizontally oriented electric field exists between stencil screen 20 and back electrode 14 so as to aid toner particles 46 in reaching the substrate.

A receptacle 48 is located beneath apparatus for receiving used developer and/or toner after it has passed through the electric field located between base electrode 12 and stencil screen 20. This material can be recirculated up to reservoir 36 by hand or by other suitable means which may include apparatus for adding additional toner to the mixture.

After completion of the printing or coating opera tion, switch 18 may be opened and substrate 30 is removed from apparatus 10 in the direction of the arrow 52, as is shown in FIG. 2.

While substrate 30 is shown as being formed of electrically non-conductive material, conductive substrates may also be printed or coated by having such substrates perform the function of back electrode 14.

Back electrode 14 may also be replaced by a suitable corona charging unit which will deposit ions of the proper polarity upon substrate 30 in order to attract toner particles onto the substrate.

Therate of developer flow is determined by the width of slot 38, the angle at which the sides of reservoir 36 slope toward the slot 38, the material and size of the carrier particles and toner particles, and the amount of toner in the developer mixture 44. Achieving proper flowability of some developers from the reservoir 36 may require the use of flow-control means, vibrators, or the use of compressed air flowing through the developer mixture to relieve a slight vacuum created by the developer flow.

The electrically conductive carrier particles touch either the base electrode 12 or the stencil screen and are charged, by conduction,'to the potential of the element touched. Substantially all of the carrier in a falling curtain oscillates, whereas in a horizontal or inclined orientation only the top few layers oscillate. Because gravity does not impede carrier oscillation and because more carrier oscillates, more toner is available for printing, thus increasing the toner deposition rate. Increasing the toner deposition rate increases the flexibility of the apparatus in that more toner can be deposited in a given period of time, print and clean voltages can be lowered, and developer concentration can be reduced.

A second embodiment of the invention is shown in FIG. 3 which includes essentially the same elements except that a second stencil screen 60 replaces base electrode 12. In addition, a second back electrode 62 is re- I quired to establish a third horizontally oriented electric field between the stencil screen 60 and back electrode 62. A second substrate 64 can then be suported upon suitable support means 66.

A power source 68, which may be 10 kilovolts, is connected to stencil screens 20 and 60, while other power sources 69 and 70, which may be 5 kilovolts, are connected to electrodes 14 and 62, so that the polarities of back electrodes 14 and 62 are always of the same polarity relative to stencil screens 20 and 60.

4 Switch means 72 is illustratedja's being a double pole, double throw switch. The switch means may take other forms such as, for example, an-electronic'switch, possibly controlled by a multi-vibrator capable of, limiting pulses to approximately one-tenth of a second. ,Switch means 72 is provided for alternately switching the polarities of stencil screens 20 and 60 relative to one another without changing the polarities of back electrodes l4 and 62 relative to their adjacen tfstencil screen. v v V v A known type of developer mixture 44 includes electrically conductive carrier particles and electrically non-conductive toner particles which are so located in a triboelectric series that the non-conductive toner particles are negatively charged. When stencil screen 20 is positive relative to stencil screen 60, a falling curtain of developer 44 will oscillate between the two stencil screens and cause toner to be deposited upon stencil screen 20 and upon substrate 30. When switch means 72 is reversed, toner will be deposited on stencil screen and on substrate 64; simultaneously, an important feature of the invention is that previously deposited negative toner will be cleaned from the now negative stencil screen 20. I

A modification of the invention of FIG. 3 is shown in FIG. 3a wherein a power source 74 is comprised of a source of alternating current. When using a developer mixture of conductive carrier and non-conductive toner, negatively charged toner will be deposited upon stencil screen 20 and substrate 30 when stencil screen 60 is negative; at the same time, stencil screen 60 will be cleaned by bombardment of carrier particles which, in a broad sense, agitate screen 60 to overcome imaging forces and Van der Waal forces and allow negative toner to come free of and be repelled from the negatively charged screen 60. Comparable results are obtained on the reverse portion of the alternating cycle with respect to stencil screen 20.

When it is desired to use electrically conductive toner with the apparatus of FIG. 3, it is unnecessary to provide switching means 72 because stencil screens 20 and 60 do not become dirty during a printing operation. As is shown in FIG. 3b, a power source 76 and voltage divider 78 are connected to the stencil screens and back electrodes. It is preferred that stencil screen 20 and back electrode 14 respect to the stencil screen 60, and the potential on the back electrode 14 being somewhat greater than the potential on the stencil screen 20. Similarly, the stencil screen 60 and the back electrode 62 are preferably held at an opposite polarity with respect to the polarity of the stencil screen 20, the potential on the back electrode 62 being somewhat greater than the potential on the stencil screen 60.

A third form of the invention is illustrated in FIGS. 4-7 as being a bench-top printer or coater 80 which includes a toner reservoir 82, best shown in FIGS. 4 and 7, which is used to create a tubular curtain which falls between reservoir 82 and a catch receptacle 84.

Apparatus 80 includes a pivotally mounted door 86 for providing access into the interior. Support wires 88 are used for supporting thereon the apparatus shown in FIG. 5 which includes a pedestal 90 for supporting a non-planar substrate such as beverage container 92. An annular stencil screen 94 is telescoped downwardly over container 92 prior to insertion of the elements within apparatus 80. Base electrode means are probe held at one polarity with vided by non-planar base electrodes 96 which are spaced from stencil screen 94 to provide an annular passageway for an annular falling curtain of developer or toner from reservoir 82. The developeror toner will then oscillate between stencil screen 94 and base electrode 96 and cause toner to pass inwardly through stencil screen 94 and become deposited upon the container or substrate 92. Excess developer or toner will then pass into catch receptacle 84 by passing through elongated openings 98 in pedestal 90.

Reservoir 82 is provided with a conical member 110 which may be adjustably positioned upwardly or downwardly, by any suitable means, to vary the size of an opening 1 12 for controlling the amount of developer or toner which forms the falling curtain. As the toner or developer leaves reservoir 82 and passes between stencil screen 94 and base electrode 96 it is prevented from entering within annular stencil screen 94 by a suitable shield 114 positioned within the top of stencil screen 94.

If the substrate or container 92 is electrically conductive, no back electrode is necessary since an electrical connection can be made directly to the substrate. If pedestal 90 is electrically conductive, an insulative sleeve 116 is used for mounting stencil screen 94 upon the pedestal 90. v I

It is to be understood that the electrical connection for the embodiments shown in FIGS. 1 and 2, and in FIGS. 4-7, may also provide means for reversing the respective electric fieldsso that cleaning pulses may be generated between printing or coating operations so as to maintain the respective stencil screens in operating condition. Suitable connection means are shown in US. Pat. No. 3,306,193 wherein means are provided for reversing the respective polarities of the base electrode and stencil screen whenever desired.

While preferred forms and arrangements of parts have been shown in illustrating the invention, it is to be understood that various changes in detail and arrangement of parts may be made without departing from the spirit and scope of the'invention, as defined in the appended claimed subject matter.

We claim:

1. A method of electrostatically printing or coating a substrate comprising the steps of providing a stencil screen and a substrate, said stencil screen being of the type having openings therein for defining a desired pattern, placing said stencil screen and said substrate in a substantially vertically disposed orientation adjacent to each other, creating a substantially vertical free falling curtain of toner in a space adjacent to said stencil screen on the side thereof remote from said substrate and along the full extent of said openings, creating a substantially horizontally directed electric field in said space forcausing some of said toner to pass through said openings in said stencil screen and impinge upon said substrate, providing a second stencil screen and a second substrate, placing said second stencil screen in spaced relation to the first-mentioned stencil screen and placing said second substrate adjacent said second stencil screen on the side thereof remote from said first-mentioned stencil screen, and creating said falling curtain of toner so that it falls in the space between said first-mentioned stencil screen and said second stencil screen.

2. The method defined in claim 1 including the step of electrically charging said. first-mentioned stencil screen and said second stencil screen to different potentials for creating an electric field in the space therebetween.

3. The method defined in claim 2 including the step of reversing the respective potentials of said firstmentioned stencil screen and said second stencil strates. 

1. A method of electrostatically printing or coating a substrate comprising the steps of providing a stencil screen and a substrate, said stencil screen being of the type having openings therein for defining a desired pattern, placing said stencil screen and said substrate in a substantially vertically disposed orientation adjacent to each other, creating a substantially vertical free falling curtain of toner in a space adjacent to said stencil screen on the side thereof remote from said substrate and along the full extent of said openings, creating a substantially horizontally directed electric field in said space for causing some of said toner to pass through said openings in said stencil screen and impinge upon said substrate, providing a second stencil screen and a second substrate, placing said second stencil screen in spaced relation to the first-mentioned stencil screen and placing said second substrate adjacent said second stencil screen on the side thereof remote from said firstmentioned stencil screen, and creating said falling curtain of toner so that it falls in the space between said first-mentioned stencil screen and said second stencil screen.
 2. The method defined in claim 1 including the step of electrically charging said first-mentioned stencil screen and said second stencil screen to different potentials for creating an electric field in the space therebetween.
 3. The method defined in claim 2 including the step of reversing the respective potentials of said first-mentioned stencil screen and said second stencil screen.
 4. The method defined in claim 2 including the step of creating additional electric fields in the spaces between the respective stencil screens and adjacent substrates. 